This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-257896 filed on Aug. 28, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a ground contamination detector mounted on, for example, a vehicle to collect elements evaporating from contaminants such as chemical agents (for example, sarin) on the ground, analyze the collected elements with a sensor, and identify the collected elements and a contaminated location on the ground.
2. Description of the Related Art
Detecting noxious contaminants in a wide area on the ground employs a contact detector that directly touches the ground to inspect, or a noncontact detector that does not directly touch the ground to inspect.
An example of the contact detector is a color reaction detector. The color reaction detector employs a detector paper that is wound around a roller and serves as a sensor. The detector paper is brought in contact with the ground and is checked to see if it develops or changes color due to a chemical reaction with substance on the ground, to determine whether or not noxious substance is present on the ground. Another example of the contact detector sets ATR (attenuated total reflection) crystals on the ground, measures the absorption spectra and intensity of infrared rays reflected from the ATR crystals, and determines whether or not noxious substance is present on the ground.
The contact detector must move the detector paper or the ATR crystals along the ground. This is very difficult to achieve if the ground is intricately undulated. The contact detector, therefore, is appropriate only for sampling soil and analyzing the sampled soil for noxious substance. The contact detector is inappropriate for identifying a contaminated location in a wide area on the ground. The contact detector has a risk of exposing the user to a noxious gas evaporating from solid or liquid contaminants on the ground even if the user is not in direct contact with the contaminants.
The noncontact detector does not directly touch solid or liquid contaminants. The noncontact detector detects gaseous elements evaporating from noxious substance, analyzes the detected elements, and determines whether or not there is noxious substance. For example, the noncontact detector emits a laser beam to an object, analyzes a reflected beam from the object, and determines whether or not the object is noxious.
FIGS. 1A, 1B, and 1C show noncontact detectors according to related arts. FIG. 1A shows an FTIR (Fourier transform infrared) gas cell detector. An infrared source A1 emits infrared rays toward a gas cell A2. The gas cell A2 passes a gas in a direction Z. An FTIR sensor A3 measures an absorption spectrum of the gas and detects elements of the gas.
FIG. 1B shows a DIAL (differential absorption lidar) detector. The DIAL detector B1 emits two types of laser beams toward the ground 1, the laser beams being adjusted for an absorption wavelength and a non-absorption wavelength of gas. The laser beams pass through a gas evaporating from noxious substance B2 and are reflected from the ground 1. The DIAL detector B1 measures contrast between the reflected laser beams and determines whether or not there is noxious substance.
FIG. 1C shows a Raman scattering detector. A laser source C1 emits a laser beam toward the ground 1, and sensors C31 to C3n measure the Raman scattering wavelengths xcex1 to xcexn of reflected beams from the ground 1. According to the measured wavelengths xcex1 to xcexn, the Raman scattering detector determines whether or not there is noxious substance.
Unlike the contact detectors, the noncontact detectors are relatively easy to detect a contaminated location in a wide area on the ground. Among the noncontact detectors, the FTIR gas cell detector of FIG. 1A and the DIAL detector of FIG. 1B measure a gas evaporating from noxious substance and floating in a space between the detectors and the ground. For these detectors, it is difficult to identify an exact location on the ground where the noxious substance is present. The reason of this will be explained with reference to FIG. 2.
FIG. 2 is a plan view showing a relationship between a location where noxious substance is present and a location where a gas evaporating from the noxious substance is detected. The noxious substance is at a location Axe2x80x2, to produce a noxious gas. The noxious gas drifts due to a wind blowing in a direction Y and scatters over an area Bxe2x80x2. Any one of the detectors of the related arts positioned at an observation location Cxe2x80x2 in the area Bxe2x80x2 may detect the drifting noxious gas. In this case, the detector is unable to identify the location Axe2x80x2 actually contaminated with the noxious substance.
It is known that the Raman scattering detector of FIG. 1C is unable to detect a wet state of the ground, i.e., unable to detect liquid contaminants soaked in the ground. If an object to detect is liquid, the Raman scattering detector requires the object to be a puddle of liquid. Namely, the Raman scattering detector is impractical for detecting noxious substance in a wet state on the ground.
The present invention provides a ground contamination detector capable of operating on noxious substance in a wet state on the ground, to correctly and speedily detect the noxious substance and a true location thereof on the ground in a noncontact manner.
According to an aspect of the present invention, a ground contamination detector has a space enclosing unit having an annular opening to blow air toward the ground to form an enclosed space on the ground, a suction pipe extending into the enclosed space and having an opening oriented toward the ground to suck a gas from the enclosed space, and a sensor to detect elements of the sucked gas.
According to this aspect, the ground contamination detector forms an enclosed space on the ground to prevent external noxious substance from entering the enclosed space, secures a noncontact state, and identifies a location of the enclosed space on the ground. The suction pipe collects a gas from the enclosed space, and the sensor detects elements of the collected gas. This detector is capable of speedily and correctly identifying a contaminated location on the ground even if the location is in a wet state.